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How to do wet etching
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© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 1
Rochester Institute of TechnologyMicroelectronic Engineering
ROCHESTER INSTITUTE OF TECHNOLOGYMICROELECTRONIC ENGINEERING
Wet Etch for Microelectronics
Dr. Lynn Fuller webpage: http://people.rit.edu/lffeee Microelectronic Engineering
Rochester Institute of Technology 82 Lomb Memorial Drive Rochester, NY 14623-5604 Tel (585) 475-2035 Fax (585) 475-5041
email: Lynn.Fuller@rit.edu microE webpage: http://www.microe.rit.edu
4-10-2008 wetetch.ppt
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 2
Rochester Institute of TechnologyMicroelectronic Engineering
OUTLINE
Wet Etch BasicsEtching of OxideEtching of NitrideEtching of SiliconEtching of MetalsRCA CleanWet Removal of PhotoresistPackage DecappingDefect DelineationCleaningReferences
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
TERMINOLOGY
Etching - the process by which material is removed from a surfaceMask Layer - Used to protect regions of the wafer surface. Examples are photoresist or an oxide layerWet Etching - substrates are immersed in a reactive solution (etchant). The layer to be etched is removed by chemical reaction or by dissolution. The reaction products must be soluble and are carried away by the etchant solution.Dry Etching - Substrates are immersed in a reactive gas (plasma). The layer to be etched is removed by chemical reactions and/or physical means (ion bombardment). The reaction products must bevolatile and are carried away in the gas stream.Anisotropic - etch rate is not equal in all directions.Isotropic - etch rate is equal in all directions.Selectivity - the ability to etch desired film but not etch underlying substrate or mask layer.Aspect Ratio - ratio of an etch geometries depth to width.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 4
Rochester Institute of TechnologyMicroelectronic Engineering
WET ETCH BASICS
Concentration: Often expressed as a weight percentage. That is the ratio of the weight of solute in a given weight solution. For example a solution containing 5 gms of solute in 95 grams of solvent is a 5 % solution.
Molarity: concentration expressed as moles of solute in 1 liter of solution. A solution containing one mole of solute in 1 liter of solution is termed a molar (1M) solution. A mole is the molecular weight in grams. Example: 10 gms of sulfuric acid in 500 ml of solution. H2SO4 has molecular weight of 1x2+32+16x4=98 so 10gms/98gm/M = 0.102M and 500ml is 1/2 liter, so this solution is 0.204 Molar
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
WET ETCH BASICS
Normality: concentration expressed as equivalents of solute in 1 liter of solution. One equivalent of a substance is the weight (1) which (as an acid) contains 1 gram atom of replaceable hydrogen; or (2) which (as a base) reacts with a gram atom of hydrogen; or (3) which (as a salt) is produced in a reaction involving 1 gram atom of hydrogen. Example 36.5 g of HCl contains 1 g atom of replaceable hydrogen and is an equivalent. 40 g of NaOH will react with 36.5 g of HCL which contains 1 g atom of hydrogen thus 40 g of NaOH is an equivalent. 98 grams of H2SO4 contains two gram atoms of hydrogen so 98/2 = 49 is one equivalent.
How many gams of sulfuric acid are contained in 3 liters of 0.5Nsolution?(answer: 74.5g)
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 6
Rochester Institute of TechnologyMicroelectronic Engineering
ISOTROPIC AND ANISOTROPIC ETCHING
Isotropic Etching - etches at equal rate in all directions
Anisotropic Etching - etches faster vertically than horizontally
Wet Chemical Etching - is isotropic (except in crystalline materials)
Plasma Etching (Dry Etch or Reactive Ion Etching, RIE) - is either isotropic or anisotropic depending on ion energyand chemistry of etch.
Film to be etched
Photoresist
Substrate
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 7
Rochester Institute of TechnologyMicroelectronic Engineering
SELECTIVITY
Rf = etch rate for nitride filmRpr = etch rate for photoresistRox = etch rate for pad oxide
Silicon
RfNitride
Photoresist
RprRox
We want Rf high and Rpr, Rox low
Selectivity of film to Photoresist = Rf/RphSelectivity of film to pad oxide = Rf/Rox
Pad Oxide
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
UNIFORMITY
Example: Calculate the average etch rate, etch rate uniformity given the etch rates at center, top left, top right, bottom right, bottom left are 750, 812, 765, 743, 798 nm
Answer: 773.6 nmand 4.4%
Etch rate uniformity (%)= (Maximum etch rate-Minimum etch rate)
(Maximum etch rate+Minimum etch rate)x100%
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 9
Rochester Institute of TechnologyMicroelectronic Engineering
DI WATER
City Water InMixed Bed FilterWater SoftenerCharcoal FilterHeat ExchangerReverse Osmosis Filters (6 Mohm)Storage TankRecirculation PumpsResin Bed Filters (Rho = 18 Mohm)Ultraviolet Light Anti Bacteria SystemFinal 0.2 um Particulate FiltersSpecial Piping
DI Water Plant at RIT
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 10
Rochester Institute of TechnologyMicroelectronic Engineering
RINSE TANKS
Cascade Rinser
Dump RinserSpin Rinse Dry (SRD)
2nd Rinse1st Rinse
DI InDrain
DI In DrainDrain
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 11
Rochester Institute of TechnologyMicroelectronic Engineering
WET ETCHING OF SILICON DIOXIDE
HF with or without the addition of ammonium flouride (NH4F). The addition of ammonium flouride creates a buffered HF solution (BHF) also called buffered oxide etch (BOE). The addition of NH4F to HF controls the pH value and replenishes the depletion of the fluoride ions, thus maintaining stable etch rate.
SiO2 + 6HF = H2SiF6 + 2H2O
Types of silicon dioxide etchants:49% HF - fast removal of oxide, poor photoresist adhesionBHF - medium removal of oxide, with photoresist mask Dilute HF - removal of native oxide, cleans, surface treatmentsHF/HCl or HF/Glycerin mixtures – special applications
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
TYPES OF BHF
7:1 NH4F/HF gives about1000 Å/min etch rate at room T
7 Parts 40% NH4Fand 1 part 48% HF
ETCH RATES FOR VARIOUS TYPES OF SiO2Thermal SiO2 BOE (7:1) 1,000 Å/min *
1:1 HF:HCl 23,000 Å/min**49% HF 18,000 Å/min #KOH@ 72 °C 900 Å/min*KOH @ 90 °C 2500 Å/min*
CVD SiO2 (LTO) BOE (7:1) 3,300 Å/min #1:1 HF:HCl 6,170 Å/min #49% HF
P doped SiO2 BOE (7:1) 2000 Å/min(spin-on dopant) 1:1 HF:HCl 25,000 Å/min
(Photoresist adhesion problems) 49% HFBoron doped SiO2 BOE (7:1) 200 Å/min*
(spin-on dopant) 1:1 HF:HCl49% HF
Phosphosilicate Glass (PSG) BOE (7:1) 10,000 Å/min #1:1 HF:HCl 11,330 Å/min #49% HF 28,000 Å/min
* RIT data, Dr. Fuller, et.al.# from Madou Text** from Journal of MEMs, Dec.’96, Muller, et.al.
* RIT data, Dr. Fuller, et.al.# from Madou Text** from Journal of MEMs, Dec.’96, Muller, et.al.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
MEASURED ETCH RATES FOR OXIDE AT RIT
Rochester Institute of Technology Dr. Lynn FullerMicroelectronic Engineering
Summary of Etch Rates and Deposition Rates for RIT Processes
Wet Etch Process Description Date Rate Units Comment7:1 Buffered Oxide Etch of Thermal Oxide, 300°K 12/1/04 1122 Å/min EMCR65010:1 Buffered Oxide Etch of Thermal Oxide, 300°K 10/15/05 586 Å/min Mike Aquilino10:1 BOE Etch of PECVD TEOS Oxide, no anneal, 300°K 10/15/05 2062 Å/min Mike Aquilino10:1 BOE Etch of PECVD TEOS Oxide, anneal 1000C - 60 min, 300°K 10/15/05 814 Å/min Mike Aquilino10:1 BOE Etch of PECVD TEOS Oxide, anneal 1100C - 6 hr, 300°K 10/15/05 562 Å/min Mike AquilinoPad Etch on Thermal Oxide, 300 °K 12/1/04 629 Å/min EMCR650Pad Etch of PECVD TEOS Oxide, 300°k 6/8/06 1290 Å/min Dale EwbankHot Phosphoric Acid Etch of Thermal Oxide at 175 °C 10/15/05 <1 Å/min Mike AquilinoHot Phosphoric Acid Etch of TEOS Oxide, no anneal, at 175 °C 10/15/05 17 Å/min Mike AquilinoHot Phosphoric Acid Etch of TEOS Oxide, 1000 C 60 min Anneal, at 175 °C 10/15/05 3.3 Å/min Mike AquilinoHot Phosphoric Acid Etch of TEOS Oxide, 1100 C 6 Hr Anneal, at 175 °C 10/15/05 3.8 Å/min Mike AquilinoHot Phosphoric Acid Etch of Si3N4 at 175 °C 11/15/04 82 Å/min EMCR65050:1 Water:HF(49%) on Thermal Oxide at room T 10/15/05 187 Å/min Mike Aquilino50:1 Water:HF(49%) on PECVD TEOS Oxide, no anneal, at room T 10/15/05 611 Å/min Mike Aquilino50:1 Water:HF(49%) on PECVD TEOS Oxide, anneal 1000 C -30 min, at room T 10/15/05 115 Å/min Mike Aquilino50:1 Water:HF(49%) of PECVD TEOS Oxide, anneal 1100C - 6 hr, 300°K 10/15/05 107 Å/min Mike AquilinoKOH 20 wt%, 85 °C, Etch of Si (crystaline) 2/4/05 30 µm/min EMCR870KOH etch rate of PECVD Nitride (Low σ) 2/4/05 10 Å/min EMCR870
See http://people.rit.edu/lffeeetools and processes
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
BUFFERED OXIDE ETCH TANK
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
ETCHING GLASS OVER ALUMINUM WITH BOE AND GLYCERIN MIXTURE
In multilevel metal processes it is often necessary to etch viasthrough an insulating interlevel dielectric. Also if chips are given a protective overcoat it is necessary to etch vias through the insulating overcoat to the bonding pads. When the underlying layer is aluminum and the insulating layer is glass the etchant needs to etch glass but not etch aluminum. Straight Buffered HF acid will etch Aluminum.
A mixture of 5 parts BOE and 3 parts Glycerin works well. Etchrate is unaffected by the Glycerin. Original work was published by J.J. Gajda at IBM System Products Division, East Fishkill Facility, Hopewell Junction, NY 12533
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
BOND PAD ETCHES FROM TRANSENE
Silox Vapox III – TRANSENE CO. (www.Transene.com)
This etchant is designed to etch deposited oxides on silicon surfaces. These oxides are commonly grown in vapox silox or other LPCVD devices and differ radically from their thermally grown cousins in many important ways. One way is their etch rate another is their process utility. The deposited oxide is many times used as a passivation layer over a metallized silicon substrate. Silox VapoxEtchant III has been designed to optimize etching of a deposited oxide used as a passivation layer over an aluminum metallized silicon substrate. This etchant has been saturated with aluminum to minimize its attack on the metallized substrate.
Deposited Oxide (Vapox/Silox) Etch Rate: 4000 Å / minute @ 22 °C
This product contains:Ammonium FluorideGlacial Acetic AcidAluminum corrosion inhibitorSurfactantDI Water
Pad Etch Measured etch rates at RIT:Thermal Oxide 630 Å/minTEOS PECVD TEOS Oxide 1290 Å/min
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
MAKING SMALL (2µm x 2µm) CONTACT CUT BY WET ETCH
Contact Cut Lithography is difficult because of the complicated film stack. The contacts are through 4000Å TEOS oxide on thermal oxide on poly on gate oxide. The poly has a silicide layer in the Advanced CMOS process. The poly thickness might be 4000Å or 6000Å. The TEOS may be annealed. Other contacts are to drain and source through 4000Å TEOS on thermally grown oxide of ~500Å (from poly reox step) plus gate oxide. The gate oxides are 330Å, 150Å, or 100Ådepending on the exact process.
Contact cut etch is also difficult. Plasma etch is difficult because of the different oxide layers and thickness and the poor selectivity between etching oxide and the underlying poly or drain/source silicon. Wet etch has problems with blocking. That is where the BOE can not get into the small contact cut openings. Blocking depends on surface tension as measured by the wetting angle which depends on the type of photoresist used.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
MAKING SMALL (2µm x 2µm) CONTACT CUT BY WET ETCH
To ensure that the photoresist is cleared in the bottom of all the contact cuts the exposure dose is increased to 285 mj/cm2 and track develop time is increased to 3 min. This makes the 2µm x 2µm contacts a little larger ~2.2µm by ~2.2µm but they are clear regardless of the underlying film stack.
Contact Cut After Photo
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 20
Rochester Institute of TechnologyMicroelectronic Engineering
MAKING SMALL (2µm x 2µm) CONTACT CUT BY WET ETCH
Wet etch has problems with blocking. That is where the BOE can not get into the small contact cut openings. Blocking depends on surface wetting angle. If blocking occurs some contact cuts will etch and clear while others will not etch as illustrated in the pictures above.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 21
Rochester Institute of TechnologyMicroelectronic Engineering
MAKING SMALL (2µm x 2µm) CONTACT CUT BY WET ETCH
To overcome the blocking problem we raised the boat completely out of the BOE every 15 seconds throughout the entire etch. To be sure to clear all the contacts the etch time was extended to 5 minutes (approximately twice the expected etch time based on etch rates and approximate film thicknesses) This approach gave excellent results for all the various film stacks as shown in the pictures above.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
SILICIDE ETCHES
Courtesy of SMFL
Etching of Ti Metal:
Heat the Sulfuric Acid:Hydrogen Peroxide (1:2) mixture on a hotplate to 100°C (set plate temperature to 150°C)
Etch for 1 min 30 sec. This should remove the Ti that is on top of the silicon dioxide but not remove TiSi that was formed on the polysilicon and D/S regions. It also removes unreacted Ti metal over the TiSi on the poly and D/S regions.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
WET ETCHING OF SILICON NITRIDE
Silicon Nitride - BOE (7:1) 20A/min, 1:1 HF:HCL 120A/min, 49% HF 140 A/min165°C Phosphoric Acid 55A/min (BOE dip first
to remove oxynitride layer), etches silicon dioxide at 10 Å/min and silicon at 1Å/min
Hot phosphoric acid etch of nitride can not use photoresist as an etch mask. One can use a thin patterned oxide (or oxynitride) to act as the etch mask. Etch rate for silicon is even lower than the etch rate of oxide.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 24
Rochester Institute of TechnologyMicroelectronic Engineering
HOT PHOSPHORIC ACID ETCH OF SI3N4
The boiling point of phosphoric acid depends on the concentration of H3PO4 in water. So if you heat the solution until it boils you can find the corresponding concentration. If you operate at the boiling temperature (temperature is controlled without a closed loop control system) and the water boils off, the concentration increases making the boiling point hotter. Thus reflux condensers and drip systems replace the water to control the concentration and boiling temperature.
MORE
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
HOT PHOSPHORIC ACID NITRIDE ETCH BENCH
• Warm up Hot Phos pot to 175º• Use Teflon boat to place wafers in
acid bath • 3500Å +/-500 à 50 minutes• 1500Å +/- 500 à 25minutes• Etch rate of ~80 Å/min
• Rinse for 5 min. in Cascade Rinse• SRD wafers
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 26
Rochester Institute of TechnologyMicroelectronic Engineering
KOH ETCHING OF SINGLE CRYSTAL SILICON
KOH etches silicon along the(111) crystal plane giving a53° angle.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
KOH ETCHING OF SINGLE CRYSTAL SILICON
Si3N4 is the perfect masking material for KOH etch solution. The etch rate for Silicon Nitride appears to be zero.
When SiO2 is used as a masking layer with a KOH solution both temperature and concentration should be chosen as low as possible. LTO is not the same as thermal oxide and can be attacked by KOH at a much higher rate. KOH etch rate is about 50 to 55 µm/min at 72 °C and KOH concentrations between 10 and 30 weight %. The Si/SiO etch ratio is 1000:1 for 10% KOH at 60 °C, at 30% it drops to 200:1. The relative etch rate of doped silicon to lightly doped silicon decreases for doping concentrations above 1E19 and at 1E20 the relative etch rate is 1/100 for 10% concentration. (on (100) wafer the angle is 50.6°)
C. Strandman, L. Rosengren, H. Elderstig, and Y Backlun uses Isopropyl Alcohol (IPA) added to the KOH mixture at 30 wt% before IPA was added. 250 ml of IPA per liter of KOH was added giving an excess of IPA on the surface of etchant during etching.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 28
Rochester Institute of TechnologyMicroelectronic Engineering
KOH ETCHING OF SILICON
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
KOH ETCHING OF SILICON OXIDE
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
KOH ETCH APPARATUS
20 wt%KOH+ IPA
ThermometerProbe withglass cover
Wafer Boat
Teflon Stirrer& Guide Plate
Wafers
Controller
Hot Plate
Holes
Plastic Screwfor Handle
Teflon Cover
70°C
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
SINGLE SIDED KOH ETCH APPARATUS
Dual 4 inch wafer holder with “O”ring seal to protect outer ½ “ edge of the wafer. Integral heater and temperature probe for feedback control system. Stainless steel metal parts do not etch in KOH.
3-28-02 Fuller et.el.50 um in 57 min at 72 C
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
PICTURES OF DIAPHRAGM ETCH
20% KOH Etch, @ 72 C, 10 Hrs.
31 µm500 µm
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
WET ETCHING OF POLYSILICON
Poly – KOH etches poly at the same rate it etches single crystal silicon. Poly does not etch with 53° angle because the crystal orientation is random.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
WET ETCHING OF ALUMINUM
Aluminum - “Aluminum Etchant Type A” from Transene Co., Inc. Route 1, Rowley MA, Tel (617)948-2501 and is a mixture of phosphoric acid, acetic acid and nitric acid. Al/1%Si leaves behind a silicon residue unless the aluminum etch is heated to 50C. For multilayer metal processes it is often necessary to etch vias through an insulating interlevel dielectric. When the underlying layer is aluminum and the insulating layer is glass the preferred etchant is 5 parts BOE and 3 parts Glycerin. (straight BOE etches aluminum) See J.J.Gaida, IBM System Products Division, East Fishkill Facility, Hopewell Junction, NY 12533.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
WET ETCHING OF METALS
Nickel - Use Aluminum Etch at 50 C Temperature, Etch Rate is about 1 min for 2000 Å, The aluminum etch solution we use is "Aluminum Etchant Type A" from Transene Co., Inc. Route 1, Rowley, Mass 0196, Tel (617)948-2501 and is a mixture of phosphoric acid, acetic acid, nitric acid.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
WET ETCHING OF METALS
Chromium - CR-9 Etch, Cyantek Corp., 3055 Osgood Court, Fremont, CA 94539-5652, (510)651-3341
Gold - Gold Etch, J.E.Halma Co., 91 Dell Glen Ave, Lodi, NJ 07644
Copper - Ferric Chloride or mix Etchant from 533 ml water, add 80 ml Na2S2O3, Sodium Persulfate, (white powder, Oxidizer), prepare in glass pan, place pan on hot plate and heat to 50 C (plate Temp set at 100 C) Etch Rate ~ 1.66 µm/min Copper Coated Board about 30 min.
Platinum – Try 7ml HCl, 1ml HNO3, 8 ml H2O at 85 C approximate etch rate 450 Å/min. (seems to work as reported by Tom Brown 10-7-94)
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 37
Rochester Institute of TechnologyMicroelectronic Engineering
TYPES OF CASSETTS AND CARRIERS
Black, Blue, Red wafer cassetts:- Fluoroware PA182-60MB, PA72-40MB- STAT-PRO© 100 (polypropylene)- 6” wafers (SSI track, Canon stepper)
- 4” wafers (SVG track, GCA stepper)- DO NOT USE IN WET CHEMISTRY
Teflon Chemical Process Wafer Cassett:- Fluoroware A182-60MB- PerFluoroAlkoxy (Teflon®) – heavy, medium- High resistance to chemicals and temperature- Can be used in wet chemistry processes
(RCA clean, BOE etch, wet nitride etch, wet aluminum etch)
heavymedium
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 38
Rochester Institute of TechnologyMicroelectronic Engineering
TYPES OF CASSETTS AND CARRIERS
Metal Cassetts:- Stainless steel- Available for 6” and 4” wafers- Use on Branson Asher only- DO NOT USE IN WET CHEMISTRY
Shipping Cassette:- Empak PX9150-04- Thin high purity polypropylene- Available in 6” and 4” wafer sizes- Not for use in processing- DO NOT USE IN WET CHEMISTRY
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 39
Rochester Institute of TechnologyMicroelectronic Engineering
WET RESIST STRIP WITH BAKER PRS-1000
What steps will use wet strip?Eventually all steps after Gate Oxide Growth
Why use wet strip?Lower temperaturesNo electric field from plasmaGate oxide reliability increases
Harmful if swallowed or inhaled. Causes irritation to skin, eyes and respiratory tract.Flashpoint 96C
Explosive vapors can be formed above this temperature (sealed container)
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
BAKER PRS-1000 PHOTORESIST STRIP
Processing temperature is 95CEtch rate calculated to be 760A/min
Process designed for 1000A/min
Inhibition layer could slow etch at start10 minutes fully stripped most wafers
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 41
Rochester Institute of TechnologyMicroelectronic Engineering
PHOTORESIST DEVELOPERS
CD-26 DI water
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 42
Rochester Institute of TechnologyMicroelectronic Engineering
RCA CLEAN WAFERS
DI waterrinse, 5 min.
H20 - 50HF - 160 sec.
HPMH2O–4500mlHCL-300ml
H2O2 – 900ml75 °C, 10 min.
SPIN/RINSEDRY
APMH2O – 4500ml NH4OH–300mlH2O2 – 900ml75 °C, 10 min.
DI waterrinse, 5 min.
DI waterrinse, 5 min.
PLAY
ANSWER
What does RCAstand for?
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 43
Rochester Institute of TechnologyMicroelectronic Engineering
ETCHING THE DUAL-IN-LINE PLASTIC PACKAGE OFF OF PACKAGED CHIPS (DECAPSULATING)
Hot H2SO4 will etch the plastic package and not etch the metal wire bonds or other metal parts as long as no water is present. Straight H2SO4 heated to 100 C for 3 hours to remove all water. Allow to cool to 80C. This etch will remove a plastic package in 30 minutes. Immerse briefly in room temperature H2SO4 to cool the part, then rinse in DI water.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
ETCH FOR SILICON DEFECT DELINEATION
Sirtl Etchant: 1 part 49%HF, 1 part CrO3 (5M) (ie 500 g/liter)Etch rate ~3.5um/min. good on (111), poor on (100) faceted pits.
Secco Etchant: 2 parts 49%HF, 1 part K2Cr2O7 (0.15M) (ie 44 g/liter). Etch rate ~1.5 um/mon. Best with ultrasonic agitation. Good on all orientations. Non-crystallographic pits.
Wright Jenkins Etchant: 2 parts 49%HF, 2 parts conc. Acetic acid, 1 part con. Nitric acid, 1 part CRO3 (4M) (ie 400 g/liter), 2 part Cu(NO3)2 +3H2O (0.14M) (ie 33 g/liter). Etch rate ~1.7 um/min. Faceted pits, good shelf life.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 45
Rochester Institute of TechnologyMicroelectronic Engineering
MASK CLEANING SOLUTION
CA-40 Photomask Cleaning SolutionUsed as a soap with texwipe similar to cleaning dishes.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
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Rochester Institute of TechnologyMicroelectronic Engineering
CLEANING SOLUTIONS
Used for CMP clean. Used as a soap with texwipe similar to cleaning dishes.
Used in dishwasher.
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 47
Rochester Institute of TechnologyMicroelectronic Engineering
REFERENCES
1. H.Seidel, L. Csepregi, A. Heuberger, and H. Baumgarel, “Anisotropic etching of crystalline silicon in alkaline solutions,” J. Electrochem. Soc., 1990, vol. 137, pp. 3612-3626.
2. Kirt Williams and Richard Muller,“Etch Rates for Micromachining Processing”, Journal of MicroelectromechanicalSystems, Vol.5, No.4, December 1996
3. Kirt Williams and Richard Muller,“Etch Rates for Micromachining Processing, Part 2”, Journal of Microelectromechanical Systems, Vol.12, No.6, December 2003
4. Scotten W. Jones and Steven T. Walsh, Wet Etching for Semiconductor Fabrication, Private Publication.
5. Buffat, Lucey, Yalamanchili, Hatcher, “Hot Phosphoric Acid APC for Silicon Nitride Etch,” Semiconductor International, August 2002, www.semiconductor.net
6. Transene Co. www.Transene.com
MORE
MORE
MORE
MORE
MORE
© April 10, 2008, Dr. Lynn Fuller
Wet Etch
Page 48
Rochester Institute of TechnologyMicroelectronic Engineering
HOMEWORK
1. Determine the etch rates for the following materials and etches:Thermal Oxide at room T in Pad EtchThermal Oxide at room T in BOE 7:1Thermal Oxide at room T in 50:1 DI:HFPECVD TEOS Oxide at room T in Pad EtchPECVD TEOS Oxide at room T in BOE 7:1PECVD TEOS Oxide at room T in 50:1 DI:HF
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